1. Field of the Invention
The present invention relates generally to a reinforcement for a concrete structure. More specifically, the invention relates to a fiber reinforced plastic (FRP) reinforcement for a concrete structure.
2. Description of the Related Art
Steel have been commonly employed as reinforcements for concrete and pre-casted concrete. However, in the recent years, sea sand comes to be mixed with a concrete as aggregate to cause severe problem of corrosion of the steel as the reinforcement due to salt component and so forth adhering thereon. Once corrosion of the steel is caused, a bonding force between the steel and the concrete can be lowered or a crack or so forth can be caused in the concrete construction due to expansion of volume of the steel due to corrosion to result in degradation of durability of the concrete construction.
As a solution to this problem, corrosion resistive FRP rods becomes to be employed as the reinforcement for the concrete.
As in the steel reinforcements, the FRP reinforcement for the concrete is provided with the outer peripheral surface having uneven profile for strengthening bonding with the concrete. As shown in FIGS. 9 and 10, the conventional FRP reinforcement is formed with the uneven profile by a cutting process on the outer peripheral surface. Also, FIG. 11 shows the FRP reinforcement disclosed in Japanese Unexamined Utility Model Publication No. 62-140115, which is formed by winding a FRP strip d on a core of a FRP rod c and bonding thereon for forming projected portions.
Among these conventional FRP reinforcement for the concrete, the former, illustrated in FIGS. 9 and 10, encounters a problem of lowering of a tensile strength of the FRP per se since the reinforcing fiber forming a rod a can be cut during processing of grooves b. Furthermore, in this prior art, since the reinforcing fiber is cut, the core portion and the projected portions are bonded only by a matrix resin. Therefore, when such FRP rod is used as reinforcement for the concrete, it cannot be expected to increase resistance against shearing stress to be exerted between the core and the projected portion due to various load applied to the concrete structure.
On the other hand, the latter, illustrated in FIG. 11, may avoid lowering of the tensile strength of the FRPs per se which form the rod of the core c and the strip d forming the projected portions. However, even in this case, since the core c and the projected portion d are bonded by resin, it still encounters a problem in a resistance against the shearing stress.
Similar defect may raise a problem even when such reinforcement is employed in the pre-casted concrete. In case of the pre-casted concrete, by releasing of tension after curing of the concrete, a residual stress will be remained on the reinforcement so that a large shearing force is exerted between the core and the projected portion to potentially cause peeling off.